8CIOPTICON MANUAL. 45 



Taking the instrument under his left arm, he should 

 go up pretty close to the screen, and adjust the focus 

 with his right hand; the image of course will be very 

 small; he must then walk slowly backwards, at the same 

 time adjusting the focus. As the image increases in size, 

 it will appear to the spectators to be coming towards 

 them; and then again let him walk up towards the 

 screen, thus diminishing the image, and it will appear 

 to them as if receding. The screen not being seen, the 

 image appears to be suspended in the air, and! the de- 

 ception is complete, even to those accustomed to the 

 exhibition. The focusing is most evenly and easily 

 effected by prying the extension; front out and in with 

 the thumb and fingers of the- right hand. 



Slides producing the best phantasmagoria^ effect are 

 those containing but one or two- figures with, a black 

 background. In ancient times, the images from the 

 phantasmagoria were thrown on the smoke arising from 

 a chafing dish in which odors and drugs were burning, 

 and by means of which many surprising and; apparently 

 supernatural effects were produced.. As a, relief &om 

 so closely following practical details, let us advert to 

 the probable use made by ancient magicians, necro- 

 mancers, and sorcerers,, of these optical contrivances 

 for producing supernatural illusions. In this w cannot 

 do better than to quote from that eminent authority on 

 optical science, Sir David Brewster : 







" In the imperfect accounts wliich have reached us of these rep- 

 resentations, we can trace all the elements of optical illusion. In 

 the ancient temple of Hercules, .at Tyre, Hny N mentions that there 

 was a seat made of consecrated stone, 'from .which the gods easily 

 arose.' Esculapius often exhibited hirnself, to, his worshipers in 

 the temple at Tarsus ; ; and the Temple a.t.Enguinum^in. Sicily, was 



